@article{Schoenfeld1980,
author = {Schoenfeld, D.},
title= {Chi-squared goodness-of-fit tests for the proportional hazards regression model},
year = {1980},
doi = {10.1093/biomet/67.1.145},
journal = {Biometrika },
volume = {67},
number = {1},
pages = {145−153},
}